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Mon, 30 Oct 2023 10:31:55 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFOw2pwrz3emhHHPGzRcEZaKdyXE5ETYrjkl0hP08/axAOlUIY6MyqVTu78CJe3u248QTKzww== X-Received: by 2002:a05:600c:3b13:b0:405:3455:567e with SMTP id m19-20020a05600c3b1300b004053455567emr8489569wms.5.1698687114826; Mon, 30 Oct 2023 10:31:54 -0700 (PDT) Received: from [192.168.1.174] ([151.81.68.207]) by smtp.googlemail.com with ESMTPSA id c5-20020a05600c0a4500b004094d4292aesm449246wmq.18.2023.10.30.10.31.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 30 Oct 2023 10:31:54 -0700 (PDT) Message-ID: <0731604e-8692-4c51-9427-78b4c629f9e9@redhat.com> Date: Mon, 30 Oct 2023 18:31:50 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v13 18/35] KVM: x86: "Reset" vcpu->run->exit_reason early in KVM_RUN To: Sean Christopherson , Marc Zyngier , Oliver Upton , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexander Viro , Christian Brauner , "Matthew Wilcox (Oracle)" , Andrew Morton References: <20231027182217.3615211-1-seanjc@google.com> <20231027182217.3615211-19-seanjc@google.com> From: Paolo Bonzini Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kvm@vger.kernel.org, David Hildenbrand , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Chao Peng , linux-riscv@lists.infradead.org, Isaku Yamahata , Xiaoyao Li , Wang , Fuad Tabba , linux-arm-kernel@lists.infradead.org, Maciej Szmigiero , Michael Roth , Ackerley Tng , David Matlack , Vlastimil Babka , =?UTF-8?B?TWlja2HDq2wgU2FsYcO8?= =?UTF-8?Q?n?= , Isaku Yamahata , Quentin Perret , kvmarm@lists.linux.dev, linux-mips@vger.kernel.org, Jarkko Sakkinen , Yu Zhang , "Kirill A . Shutemov" , kvm-riscv@lists.infradead.org, linux-fsdevel@vger.kernel.org, Liam Merwick , Vishal A nnapurve , linuxppc-dev@lists.ozlabs.org, Xu Yilun , Anish Moorthy Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 10/27/23 20:22, Sean Christopherson wrote: > Initialize run->exit_reason to KVM_EXIT_UNKNOWN early in KVM_RUN to reduce > the probability of exiting to userspace with a stale run->exit_reason that > *appears* to be valid. > > To support fd-based guest memory (guest memory without a corresponding > userspace virtual address), KVM will exit to userspace for various memory > related errors, which userspace *may* be able to resolve, instead of using > e.g. BUS_MCEERR_AR. And in the more distant future, KVM will also likely > utilize the same functionality to let userspace "intercept" and handle > memory faults when the userspace mapping is missing, i.e. when fast gup() > fails. > > Because many of KVM's internal APIs related to guest memory use '0' to > indicate "success, continue on" and not "exit to userspace", reporting > memory faults/errors to userspace will set run->exit_reason and > corresponding fields in the run structure fields in conjunction with a > a non-zero, negative return code, e.g. -EFAULT or -EHWPOISON. And because > KVM already returns -EFAULT in many paths, there's a relatively high > probability that KVM could return -EFAULT without setting run->exit_reason, > in which case reporting KVM_EXIT_UNKNOWN is much better than reporting > whatever exit reason happened to be in the run structure. > > Note, KVM must wait until after run->immediate_exit is serviced to > sanitize run->exit_reason as KVM's ABI is that run->exit_reason is > preserved across KVM_RUN when run->immediate_exit is true. > > Link: https://lore.kernel.org/all/20230908222905.1321305-1-amoorthy@google.com > Link: https://lore.kernel.org/all/ZFFbwOXZ5uI%2Fgdaf@google.com > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/x86.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index ee3cd8c3c0ef..f41dbb1465a0 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -10963,6 +10963,7 @@ static int vcpu_run(struct kvm_vcpu *vcpu) > { > int r; > > + vcpu->run->exit_reason = KVM_EXIT_UNKNOWN; > vcpu->arch.l1tf_flush_l1d = true; > > for (;;) { Reviewed-by: Paolo Bonzini